In investigations of the composition and dynamics of the earth's particulate atmosphere, particle shape is an important parameter by which classification and possibly identification of particles may often be achieved. Spherical droplets, cuboidal crystals typical of marine aerosols, and the wide variety of morphologies assumed by ice crystals, are examples where the determination of shape may be used in combination with size spectra measurements to provide experimental data upon which theoretical models of macroscopic and microscopic physical behaviour of clouds and aerosols may be developed and tested. A specific example of this involves the study of ice microphysics and the behaviour of droplets and ice crystals which can occur simultaneously within clouds. The radiative properties of these mixed-phase clouds can be radically dependent upon the relative proportions and size spectra of the two phases, as well as the orientations of the ice crystals present, and this has a profound effect upon the proportion of incident sunlight reaching the lower atmosphere and earth surface. To be able to understand the radiative transfer properties of ice and mixed phase clouds, a detailed knowledge of the particles' shapes and sizes is required, along with measurements of the number concentration of ice and super-cooled liquid water particles. Furthermore, measurement of the total ice crystal number is important to facilitate the testing of theories of the nucleation of ice crystals and their role in climate change.